Verse 5 of Surah Al-Tauba (The Repentance), Chapter 9 of the Quran....This verse tells Muslims to kill those who believe in the trinity of God.

فَإِذَا انْسَلَخَ الْأَشْهُرُ الْحُرُمُ فَاقْتُلُوا الْمُشْرِكِينَ حَيْثُ وَجَدْتُمُوهُمْ وَخُذُوهُمْ وَاحْصُرُوهُمْ وَاقْعُدُوا لَهُمْ كُلَّ مَرْصَدٍ ۚ فَإِنْ تَابُوا وَأَقَامُوا الصَّلَاةَ وَآتَوُا الزَّكَاةَ فَخَلُّوا سَبِيلَهُمْ ۚ إِنَّ اللَّهَ غَفُورٌ رَحِيمٌ

Translation:

"So, when the sacred months have passed, kill the polytheists wherever you find them and capture them and besiege them and lie in wait for them at every place of ambush. But if they repent and observe the prayer and give the obligatory charity, then leave their way free to them. Indeed, Allah is Forgiving, Merciful."

Those that believe that Jesus is the Son of God would be classified by Muslims as "polytheists", because they say Allah has no children. But we are all God's children. We that believe in Jesus do not believe in three gods, but in One: Who is the Father, the Son, and the Holy Spirit. But Muslims reject the divinity of Jesus, and so if they blindly follow what is in the Quran, they would kill us, if God permits.

Each of us is also a trinity: A soul, a physical body, and a spirit.... But yet we remain as one being. Likewise, God is One. God's Love is manifested as the Divine Man Jesus Christ, but his Spirit is infinite and everywhere. He is One God. Those who know the Truth are not polytheists, but the deceived would say so, and use that claim to justify the murder of innocent Christians.